Marconi 4816 1590 survivor!
 

About 20 years ago a friend gave me a 12" Marconi 1590 portable TV.
He told me that it had mistakenly had mains connected to the 12v battery lead..:-) ( The battery lead had been fitted with a standard 13A plug as the static caravan it was used in was wired for 12V using standard 13A sockets..)
The mains lead had been cut short and tucked inside the case.
Then one day after the set had been taken home his son had plugged it in to the mains. There had been a bang and a flash.
I kept the set purely because I thought the tuner mech would be a good spare for my 8500 one day.
It was plonked in my loft and forgotten about until fairly recently when the tuner mech in the 8500 started to jam and fall apart as they do...
I got the set from the loft with the intention of nicking the mech for a quick fix.
but once the set was on the bench, well dining room table I felt sorry for it.
I thought I would test the tube heaters as being wired across the LT line I fully expected them to be O/C in which case I would nick the tuner and scrap the rest with a relatively clear conscience. I was surprised to find that they were intact,
The 2.5 amp fuse in the set was blown to kingdom come only one end cap remained. the 13A fuse in the what was battery plug was also blown.
I had a quick check around with the AVO, reverse protection diode, smoothing cap. regulator transistor. regulator control transistor and zener diode all ok. which I found surprising.
So I replaced the fuses removed the tube base, connected the AVO across the LT line and switched on.
10 volts LT a splutter and crackle from the speaker and the sound of a 625 line timebase which I can still just about hear!
I connected the tube base and was rewarded with a slightly undersize snowy raster.
Tuning in my signal generator produced a slightly undersize crosshatch with slight foldover at the top of the picture.
Setting the LT voltage to 11volts and I had a belting picture.
The on off volume control is crunching and scratching I think the battery contacts are shattered but other that that the set has survived!
I think it is incredible that major damage had not been done. I fully expected it to totally destroyed.
So now I have a nice little Marconi portable in the collection ;D
The poor old Marconi 8500 will have to wait for a tuner mech.

Re: Marconi 4816 1590 survivor!
 

Nice work, I always rated thorn, they did some creditable stuff in the day, not like the good looking but nasty bush a823 chassis which I hated.
greg.

Re: Marconi 4816 1590 survivor!
 

They run forever and good crt.s normally.Yes any 12V input should be reverse polarity protected.

Re: Marconi 4816 1590 survivor!
 

Amazing that it survived it's ordeal almost unscathed, they are a cracking little set.
Mine was found in a house clearance some years ago, the only attention it needed was a good clean and a dose of Servisol in the pots.
Glad to see another example returned to working order.
:beer:
Mark

Re: Marconi 4816 1590 survivor!
 

These excellent sets date back to 1972, about the time I opened the shop.
Sold under the Marconiphone Ultra and Ferguson brands the set were sold in large numbers. Back then the first fault I encountered was failure of the 12volt supply rectifier diodes in the power supply, the originals weren't up to the job. Fortunately, just in time the 1N5401 series of 3amp diodes were available and were used as reliable replacements. Also, failure of certain diodes in the line output stage, seem to remember the CRT A1 diode needed replacement in early production models. BY207 was the approved replacement.
Models 4816 and 6816 remained in production until 1977.

DFWB.

Re: Marconi 4816 1590 survivor!
 

Hi.

I agree, it's incredible that the set survived after the mains was applied to the 12V input.
I liked the Thorn 1590/1 series and found them to be generally reliable. The usual Thorn cracked solder on the bar of the tuner was a common trouble spot. The LT regulator could cause hum problems due to being leaky. There were a number of production changes over the years including a change to silicon LT regulator and line output transistors which improved the reliability.
Early models had an EHT smoothing capacitor.
I remember one or two problems in the IF stages, sometimes due to transistors and other instability issues due to disc ceramic capacitors. The tubes lasted well and the LOPT was good though not above suspicion.
Miscellaneous troubles included iffy preset resistors and some carbon composition resistors going high.
I have a Ferguson badged 1590 in the loft which I hope to look at before long.

Regards
Symon.

Re: Marconi 4816 1590 survivor!
 

I've had Ferguson 1590 from new, the only faults I can recall was a hum bar due to one of the rectifiers having a dry joint and distorted sound which I haven't got round to looking at.

I modified it to take audio and video out and used the video output to feed an external teletext decoder with its own monitor. Used to receive perfect text from the Winter Hill transmitter, 80 miles away in Beaumaris on Anglesey. Not bad for a TV not designed for teletext.

Keith

Re: Marconi 4816 1590 survivor!
 

The sound distortion is usually due to the loudspeaker. J.

Re: Marconi 4816 1590 survivor!
 

Mention of sound distortion reminds me about one of these sets I had on the bench in about 1975, with sound distortion when the battery voltage fell below about 12 volts.
The problem turned out to be self-oscillation of the power regulator transistor which was of the later silicon type. It only oscillated (at H.F.) in a narrow band of supply voltages around 12 volts. A ferrite bead fitted directly onto the emitter pin of the reg. completely cured the fault. Tony.

Re: Marconi 4816 1590 survivor!
 

A hooting regulator. The humble ferrite bead if often a great fix for spurious oscillations.

Regards
Symon.

Re: Marconi 4816 1590 survivor!
 

I have a scrap 1590 set here an ultra with a bleached and distressed cabinet, I will hang onto it as such but if any spares are needed I can rob them

Re: Marconi 4816 1590 survivor!
 

Hi I would be really happy to buy the on off volume switch, knob and the battery socket. The battery socket is missing on mine as the 12 volt lead had been hard wired. The on off switch is crunching and sticking as the battery contacts have presumably melted or welded themselves, and the on off volume knob is a badly fitting replacement that looks as if it came from a 70's transistor radio.
If you wouldn't mind giving me a price inc postage by PM.
many thanks
Rich.

Re: Marconi 4816 1590 survivor!
 

well done for taking the screen shot before one of those lockfits dies!

I found one in an abandoned house some years ago which had been a TV repair shop (Cousins of Cobridge, permission to grab) and it worked as soon as all the water had been tipped out and dried. This did not make up for the fact that a day earlier the entire remaining stock of late 60s/early 70s tvs and crts had been made into a bonfire around the back.

Re: Marconi 4816 1590 survivor!
 

The Thorn 1590's are great little sets.
Good performers, work well in areas of poor signal, very robust and put up with most things that their owners threw at them and when they did go wrong they were very pleasant to work on. With that big forward facing elliptical speaker the sound was good on them as well.

Re: Marconi 4816 1590 survivor!
 

Hybrid Tellies wrote: "....and when they did go wrong they were very pleasant to work on."

Possibly the only TV set to have it's own service frame. Take the back off, turn the chassis upside down and you have the easiest TV to repair of all time.

Remember seeing pictures of radio receivers being tested in the old EMI works. The chassis was fitted into a service frame to permit easy repair and adjustment. Already fitted for service work in the 1590.

DFWB.

Re: Marconi 4816 1590 survivor!
 

Photo of parts required.

Re: Marconi 4816 1590 survivor!
 

Thanks very much Dave, just the job! I have replied to your PM.
I'm really pleased. The poor little Marconi has sat in the loft on "death row" for two decades and now it will be given a new lease of life. If the tuner on my Marconi 8500 hadn't started playing up it would have still been there.
:thumbsup:
Rich.

Re: Marconi 4816 1590 survivor!
 

Nice set - accessing the fuse was always a challenge though, especially when the light was bad! They would soldier on in kitchens with the EHT stick (early ones were enclosed) fizzing and arcing.
The speakers in the 14" never were that good - ditto the CRTs. Nice looking sets, though.
Hands up who opened what they thought was a 1590 to find - valves? The only clue was the absence of the battery socket.
Glyn

Re: Marconi 4816 1590 survivor!
 

There was another clue, the slots in the speaker grille were vertical instead of horizontal. 1580 chassis appears to be very rare now.

John.

Re: Marconi 4816 1590 survivor!
 

Agh! Yes the 1580 chassis model 3805. This must be the rarest Thorn ever produced other than the 'Transvista' an all transistor model produced in 1961.

As Glyn has posted, not many external clues. The front label says just says COURIER. The 1590 has 'Mains Battery'. The loudspeaker slots are vertical as mentioned on the 1580. The ring aerial is 'V' shaped on the 1580 and of course, no battery socket.

The odd thing is the battery socket is marked on the back but not punched through making me think this was an interim model before the release of the 1590. It must have been a very expensive retooling job for such a low production run.

The chassis is interesting, almost a cross between the 980 and a 1500. The sound output valve is a PCF80 but sounds more like an ECL80. It has good sound and superbly designed as are all Thorn chassis.

I took these pics this evening but had to change the phone camera for the off screen shot to monochrome due to the very high contrast picture causing flattening of the whites. Regards, John.